JP2000144352A - Production of aluminum foil for electrode of electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the surface condition of foil and to attain the further increase of capacitance by removing a surface layer before process annealing. SOLUTION: By thinly removing a surface layer before process annealing, the surface condition of foil obtd. after final annealing is made uniform, and, in its turn, the foil uniform in etching meltability can be obtd. The removal of the surface layer is executed preferably at the point of time when the cold draft reaches >=96%, where the cold draft is expressed by (T1-T2)/T1×100, T1 denotes the sheet thickness after hot finish rolling, and T2 denotes the material thickness at the time of the removal of the surface layer. As a method for removing the surface layer, both of chemical removing and mechanical removing may be adopted. As the chemical removal, activator cleaning is particularly preferable, and, as the activator, both of the acidic one and alkaline one may be used, and, sulfuric acid, sodium hydroxide or the like is exemplified. As the mechanical removal, liq. foaming is particularly preferable. Moreover, the amt. of the surface layer is preferably controlled to <=0.5 μm in the thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aluminum foil for an electrode of an electrolytic capacitor.

[0002] In this specification, the term "aluminum" is used to include both aluminum and its alloys.

[0003]

2. Description of the Related Art An aluminum foil used as an electrode material of an aluminum electrolytic capacitor is subjected to an electrochemical or chemical etching treatment in order to increase its effective area and increase the capacitance per unit area. In particular,
Due to the demand for downsizing parts due to product downsizing,
There is a growing need for higher capacitance.

However, a sufficient capacitance cannot be obtained simply by etching the foil. Therefore, from various viewpoints, improvements have been made to improve the etching characteristics to increase the capacitance. One such method is to control the surface state of the aluminum foil.

For example, in Japanese Patent Application Laid-Open No. 2-148711, in order to remove Fe powder adhering at the time of hot rolling and to prevent etching unevenness, the rolling reduction exceeds 96% in cold rolling after hot rolling. It is described before that the foil is washed with an alkaline solution having a pH of 10 or more for 1 to 100 seconds. In Japanese Patent Application Laid-Open No. 3-257147, the thickness (t) of an aluminum plate is set to reduce the thickness of a final oxide film of a foil.
Is rolled to a range satisfying 3.3T ≦ t ≦ 20T (T is the final foil thickness), washed with an alkaline or acidic aqueous solution, cold-rolled, and generated during hot rolling and cold rolling. It is described that a thick oxide film is removed. In Japanese Patent Application Laid-Open No. Hei 10-81945, an aluminum material having a purity of 99.96 to 99.98% is used at a temperature of 200 to 500 ° C. for the purpose of increasing the Miller index (100) plane crystal occupancy of the foil to 92% or more. For one hour or more under the above conditions, and furthermore, removing the surface layer of the foil by 0.1 μm or more after the intermediate annealing until the final annealing.

[0006]

However, even with each of the above-mentioned methods, the uniformity of the solubility of the foil surface during etching is insufficient, and it cannot meet the demand for an increase in capacitance.

The present invention has been made in view of such technical background,
An object of the present invention is to provide a method for manufacturing an aluminum foil for an electrolytic capacitor electrode, which can be expected to further increase the capacitance by controlling the surface state of the foil.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the surface layer formed during the intermediate annealing, particularly the quality of the oxide film, affects the surface state after the final annealing, and further affects the etching characteristics. And completed the present invention.

That is, in the method of manufacturing an aluminum foil for an electrolytic capacitor electrode according to the present invention, in order to achieve the above object, a plane-slurried aluminum slab is soaked, hot-rolled, and then cold-rolled. In the method for producing an aluminum foil to be subjected to intermediate annealing during the intermediate rolling and further to final annealing, the surface layer is removed before the intermediate annealing.

In the present invention, the surface layer is removed before the intermediate annealing because the intermediate layer is subjected to the intermediate annealing in a state where the rolling oil and the oxide film adhered to the surface are removed, and the surface layer formed during the intermediate annealing is formed. The purpose is to achieve uniformity. This is because if intermediate annealing is performed in the presence of a rolling oil or an oxide film, the thickness and quality of a surface layer formed by the annealing, particularly the thickness and quality of the oxide film, become non-uniform, and the oxide film is formed by subsequent cold rolling. Is embedded in the inside, and even if the surface is cleaned before the final annealing, the oxide film cannot be uniformly removed, and the oxide film cannot be homogenized by the final annealing. As a result, the solubility of the foil due to the etching becomes non-uniform, and an increase in capacitance cannot be expected.
In addition, when the solubility of the foil becomes non-uniform,
Capacitance varies in the length direction, between coils, or between lots, so that constant quality cannot be maintained.

As described above, according to the present invention, the surface state of the aluminum foil obtained after the final annealing is made uniform by thinly removing the surface layer before the intermediate annealing, and further, the aluminum foil for an electrode having uniform etching solubility is obtained. Can be manufactured.

Further, it is preferable that the timing of removing the surface layer is controlled by a cold rolling reduction expressed by the following equation.

Cold reduction rate (%) = (T1−T2) / T1 × 100 where T1: Thickness after hot finish rolling T2: Material thickness after removal of surface layer The cold reduction rate is less than 96% In this case, since the rolling reduction after the intermediate annealing becomes high, the non-uniform layer is easily formed by the subsequent cold rolling, and (10)
0) The area ratio tends to decrease, and the effect of improving the etching characteristics is weakened. For this reason, it is preferable to perform the removal of the surface layer when the cold rolling reduction is 96% or more, in which the formation of a non-uniform layer in subsequent rolling is small and the effect of improving the etching characteristics can be expected. In particular, it is preferably performed at a cold rolling reduction of 97% or more.

The method of removing the surface layer includes chemical removal,
Any of mechanical removal may be used and is not particularly limited. As the chemical removal method, any of organic solvent washing and activator washing may be used, but activator washing can remove not only the rolling oil on the material surface but also the heterogeneous oxide film formed in the rolling step. In this regard, an activator wash can be recommended. The type of activator may be either acidic or alkaline, and examples thereof include sulfuric acid, nitric acid, sodium hydroxide, and sodium phosphate. In the case of mechanical removal, shot blast,
Liquid forning and the like can be exemplified. In the case of mechanical removal, liquid forning can be recommended in that the treated finished surface is good.

Further, when the removal amount of the surface layer increases, the aluminum loss increases, and the processing time increases. Therefore, the thickness is preferably 0.5 μm or less in the thickness direction. A particularly preferred removal amount is 0.01 to 0.1 μm.

The conditions for face milling, homogenization, hot rolling and cold rolling are not particularly limited, but follow conventional methods. Also, the aluminum material may be in accordance with a conventional method for securing the uniformity of dissolution during etching as a foil for an electrolytic capacitor electrode, and it is preferable to use a high-purity material having a purity of 99.9% or more.

[0017]

Next, specific examples of the method for manufacturing an aluminum foil for an electrolytic capacitor electrode according to the present invention will be described.

First, an aluminum slab having a purity of 99.99% is subjected to face milling and soaking treatment by a conventional method, and then an ascending sheet thickness 5 mm.
mm, and then cold-rolled to obtain a foil having a thickness of 0.6 mm.

In Examples 1 to 8, the foil was rolled to each of the cold reduction rates shown in Table 1 below, and the surface layer was removed by the method and removal amount shown in Table 1. , 2
Intermediate annealing was performed under the conditions of 50 ° C. × 10 hours, and further cold-rolled to a foil thickness of 0.1 mm.

On the other hand, in Comparative Example 1, intermediate annealing was performed at the rolling reduction shown in Table 1 without removing the surface layer of the foil base, and further cold-rolled to a foil thickness of 0.1 mm. In Comparative Example 2, the surface layer was removed after the intermediate annealing. In Comparative Example 3, the reduction ratio was 95.
At 0%, the surface layer was removed, further cold-rolled to 97.5%, intermediately annealed, and further cold-rolled to a foil thickness of 0.1 mm.

The aluminum foil was 500 mm in width and 2000 m in length in both the examples and comparative examples, and was wound into a coil.

Each of the aluminum foils manufactured as described above was washed with a weak alkaline cleaning agent and then subjected to a final annealing at 500 ° C. for 1 hour in an inert gas atmosphere.

Further, these aluminum foils were heated at 75 ° C.
In a mixed solution of 1 M HCl and 3 M sulfuric acid at a current density of 20 A / dm ² And then dipped in sulfuric acid at 90 ° C. for 8 minutes for 300 seconds by EIAJ method.
After the V conversion treatment, the capacitance was measured. The capacitance was measured for each of the foil pieces sampled from six different positions in the width direction and the length direction in the coil. In Table 1, the average value of the capacitance of each aluminum foil is shown as a relative value when Comparative Example 1 is set to 100, and the variation of the capacitance depending on the position is shown by a calculated value based on the following equation.

Variation in capacitance (%) = (C _A -C
_B ) / C _X × 100 where C _A : Maximum value of capacitance C _B ： Minimum value of capacitance C _X : Average value of capacitance

[Table 1]

From the results shown in Table 1, it was confirmed that by removing the surface layer before the intermediate annealing, the capacitance could be increased and the variation in the capacitance depending on the position could be suppressed.

[0026]

As described above, the method for manufacturing an aluminum foil for an electrolytic capacitor electrode according to the present invention comprises a method comprising: soaking a surface-cut aluminum slab and subjecting it to hot rolling; In the method of manufacturing an aluminum foil to be subjected to intermediate annealing in the course of final annealing and further to final annealing, since the surface layer is removed before the intermediate annealing, the rolling oil and the oxide film formed so far were removed. Intermediate annealing is performed in the state, and the foil obtained after the final annealing has a uniform surface state. The aluminum foil having such a uniform surface also has uniform etching solubility, can increase capacitance, and can reduce variation in capacitance.

The removal of the surface layer is carried out at a cold reduction ratio of 96.
%, Or when the removal amount of the surface layer is set to 0.5 μm or less in the thickness direction, the above-described effect can be particularly remarkably exerted.

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Claims (3)

[Claims] 1. A method for producing an aluminum foil, wherein a soaked aluminum slab is soaked, hot-rolled, cold-rolled, subjected to intermediate annealing in the course of cold rolling, and further finally annealed. A method for producing an aluminum foil for an electrolytic capacitor electrode, comprising removing a surface layer before intermediate annealing. 2. The cold rolling reduction at the time of removing the surface layer is 96%.
The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, which is as described above. 3. The amount of removal of the surface layer is 0.1 in the thickness direction.
3. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the thickness is 5 μm or less.